In the manufacture of microelectronic devices, such as processors, controllers, and memory, the desired structures are formed on a wafer. Individual dies are cut from the wafer and then sealed into a package. The package has an array of pins, pads, or lands that make contact with the rest of the device, typically through a printed circuit board to allow the die to be operated while within the package. Before packaging, either as part of a wafer or an individual die, each die is tested to determine whether it has been manufactured correctly and operates as intended. In some cases, the dies are also sorted based on performance.
To perform the tests, some dies have lands or pads specifically designed into the die for test purposes. Pins or probes are applied to the lands or pads and signals are sent or received through the pins to test the die. For a more complex die, more pins are used. Similarly for denser circuitry on the die, the pins are closer together.
The test probes are attached to a substrate that holds each probe in the proper position with respect to each other probe so that when the sort interface unit is pressed against the pads on the die, each probe will contact its respective pad. The probes are resilient and have a shaped tip so that when the probes are pressed against the die the pressure will stress and break through any oxide that has formed on the surface of the wafer die bumps in order ensure good electrical contact. The tip wear with each new contact and, as a result, each test probe has a limited number of die tests that it can perform, after which it must be replaced. The replacement cost of each test probe is therefore a factor in the cost of die manufacturing.
The substrate and the probes are typically separately manufactured using a MEMS (microelectromechanical systems) process, or a process similar to how transistors are made. This process provides technology to form many different geometric shapes at the probe tip. The different tips have different abilities to concentrate stress and break through the oxide on different types of wafer die bumps. Once the probes are made, they are assembled onto a space transforming substrate.
Each probe has a curve in its middle section so that when pressed against the die it will bend. The probes must all bend in the same direction so that they do not contact each other during use, possibly creating connections that destroy the die or the probe. Several thousand to tens of thousands of probes may be needed to build one sort interface unit for a microprocessor. This number is expected to increase as die complexity and density increases from today's probe counts. The process is performed manually in part due the shape of the probe. The central curve increases the complexity of the probes being inserted and attached to the space transforming substrate in an automated process.